The long range purpose of this program is to design a better synthetic milieu in which freshly explanted or long term mammalian cells will survive and grow. Topics of present interest include: (1) the role of oxygen in survival, growth, and metabolism of cells, particularly sparse cell populations; (2) chemical analyses of a presumed-peptide growth factor for mammalian cells grown in serum-free medium; (3) the growth of human epithelial cells in vitro. BIBLIOGRAPHIC REFERENCES: Taylor, W.G. and Parshad, R.: Peptones as serum substitutes for mammalian cells in culture. Methods in Cell Biology Vol. XV, pp. 421-434, 1977. Parshad, R., Sanford, K.K., Jones, G.M., Price, F.M. and Taylor, W.G.: Oxygen and light effects on chromosome aberrations in mouse cells in vitro. Exp. Cell Res. 104: 199-205, 1977.